The present invention relates to image-transfer sheets for multiple-record service. More particularly, this invention relates to image-transfer papers for use in sets which are capable of transferring images upon impact on that surface of each paper which faces the impacting instrument so that differing records may be entered on opposite sides of manifold sets formed from image transfer sheets of this invention without backprinting on the other surface of the paper, i.e., that surface which faces away from the impact instrument.
A variety of attempts have been made in the development of "non-carbon" papers for use in manifold sets which are secured at one edge to avoid the need for assembly of such sets by the user, and to avoid the problem of smudging or smearing which is typical of carbon-type transfer sheets.
A particularly effective image transfer paper is typicafied in a series of patents to Barrett K. Green, including U.S. Pat. Nos. 2,548,366; 2,550,466; 2,550,467 and 2,618,573. Typically, these papers are mutually sensitized by the presence of image-forming reactants on adjacent sheet surfaces, at least one of the reagents being micro-encapsulated to avoid unintentional reaction between the reagents. The pressure or pinching of local areas of the papers, such as by a typewriter key and platen, is relied upon to rupture and free the micro-encapsulated reagent in the impact area, thereby causing the desired image transfer to the subjacent sheet. These non-carbon papers have proven generally satisfactory and have enjoyed commercial success, both in the simpler two-sheet sets and in manifolds in which several imaged copies are desired.
However, the non-carbon papers heretofore available have been limited to the application of images to only one side of the sheet or form, since the transfer of the imaging reactants has not been directionally controllable and, therefore, results in backprinting on the "back" of the sheet from the surface on which the image is desired, if used on the "wrong" side.
This backprinting will confuse or make illegible a subsequently desired image on the back surface, consequently precluding the use of both sides of the assembled papers. Therefore, these papers have made necessary the use of excessive numbers of sheets and have resulted in considerable costs not only for the papers themselves but also for the filing or storage of such one-side-only records.
U.S. Pat. No. 3,968,299 discloses a directional, image-transfer paper having multiple reagents for image reproduction and screening means for selectively releasing one of the reagents only in the direction of impact of the image-producing implement, e.g., a pen or typewriter key. However, to form the patented paper, it is necessary to form on a paper base the screening means, a cumbersome process.
Therefore, the prior non-carbon sheets or papers have not been found to be entirely satisfactory.